animal invaders – Page 5 – Center for Invasive Species Prevention

Invasive Earthworms Need Action!

Amynthes agrestis; National Park Service photo

Earthworms have been largely ignored as a class of invaders. But evidence is accumulating that their numbers and impacts are too significant to ignore.

Non-indigenous earthworms began arriving in the Americas with the first European colonists and they are now widespread. One study (see summary of Reynolds and Wetzel 2008 here) found 67 introduced species among the 253 earthworm species in North America (including Mexico, Puerto Rico, Hawaii, and Bermuda). In Illinois, 20 of the 38 species are introduced. Nuzzo et al. 2009 recorded a total of 11 earthworm species – all nonnative – at 15 forest sites in central New York and northeastern Pennsylvania.

Earthworms are good invaders – they reproduce quickly and are easily transported to new places – both carelessly and deliberately for bait, composting, or other uses.

As ecosystem engineers, invasive earthworms cause significant impacts to the soil and leaf litter, as well as to plants and animals dependent on those strata. However, they are little studied and few efforts been made to address their threat. Wisconsin is the pioneer (see below).

Ecosystem Engineers: Impacts on Soil, Plants, and Animals

Invasive alien earthworms cause enormous damage in forest environments. (I have seen no information about the damage they might cause in other natural systems.) Earthworms can change soil chemistry, soil structure, and the quantity and quality of the litter layer on the soil surface. Changes include rapid incorporation of leaf litter into the soil, alteration of soil chemistry, changes in soil pH, mixing among soil layers, and increased soil disturbance. Such changes have been shown to harm native plant species – both herbaceous ones on the forest floor as well as the regeneration of woody vegetation, including trees. See the review just published by Craven et al. 2016 and Hale and Nuzzo references below).

Craven et al. (2016) conducted a meta-analysis of 645 observations in earlier publications. They sought to measure the effects of introduced earthworms on plant diversity, cover of plant functional groups, and cover of native and non-native plants. Sites with a higher the diversity of invading earthworms – with associated variety in behaviors (see below) – had greater declines in plant diversity. Higher earthworm biomass or density did not reduce plant diversity but did change plant community composition: cover of sedges and grasses and non-native plant species significantly increased, and cover of native plant species (of all functional groups) tended to decrease. The increase in non-native plant cover in areas with higher earthworm biomass is thus an example of ‘invasional meltdown’ as propounded by Simberloff and Von Holle in 1999.

Craven et al. 2016 propose several direct and indirect mechanisms by which introduced worms might affect plant species. These include ingestion of seeds or seedlings, burying seeds, and alteration of water or nutrient availability, mycorrhizal associations, and soil structure. European and Asian plant species that co-evolved in the presence of earthworms could better tolerate earthworms’ presence.

Important Questions

Craven et al. 2016 note that the interaction of the invader-related factors with other site-related conditions such as deer browsing, fire history, forest management, and land-use history require further study to disentangle. Many other questions need to be answered, too.

Although Craven et al. (2016) do not specify the geographic range of the studies analyzed, I believe most were conducted in the northern and northeastern regions of the United States and some parts of Canada. It would be interesting to see if these studies’ findings differed from those carried out in Great Smoky Mountains National Park on the Tennessee-North Carolina border. The latter is an area where – unlike the northern states – earthworms were not wiped out by the most recent glaciation. (See references by Bruce Snyder and Jeremy Craft, below.)

The finding that worm species diversity is associated with decreased plant species diversity seems to indicate that worms’ impacts might vary depending on the behavior of the worm in question – especially whether the worms remain on or near the soil surface and — if not — how deeply they burrow. Are studies under way to clarify these differences?

Furthermore, do the impacts of European worms – the subjects of most of the studies carried out in Minnesota, New York, and Pennsylvania – differ substantially from the impacts of Asian earthworms? Or are any differences explained better by the species’ activity in the soil (e.g., depth of burrows) than their origins?

Impacts of earthworms on wildlife are less studied and perhaps less clear. Several studies have focused on salamanders because of their known dependence on leaf litter. In a study of 10 sites in central New York and northeastern Pennsylvania, Maertz et al. 2009 found that salamander abundance declined exponentially with decreasing volume of leaf litter. They suggested that the salamander declines were a response to declines in the abundance of small arthropods, a stable resource.

A study by Ziemba et al. (2016) in Ohio involved Asian worms (genera Amynthas and Metaphire) rather than the European worms most often included in studies carried out in Minnesota, New York, and Pennsylvania. These authors found a complex picture: earthworm abundance was negatively associated with juvenile and male salamander abundance, but had no relationship with female abundance.

Craft (2009) found that reduced leaf litter mass in invaded areas of Great Smoky Mountains National Park diminished habitat for both salamanders and salamander prey.

Others have studied millipedes – a largely unappreciated example of biological diversity in the Southern Appalachian Mountains – in Great Smoky Mountains National Park. Snyder and colleagues (2013) found that earthworms in the genus Amynthas altered soils by decreasing the depth of partially decomposed organic horizons and increasing soil aggregation. The result was a significant decrease in millipede abundance and species richness – probably as a result of competition for food.

Results from a study of earthworms’ effects on the Park’s food web by Anita Juen and Daniela Straube, begun in 2010, have not yet been published (pers. comm. from GRSM staff).

Even birds might be affected by worm invasions. One study in Wisconsin found that hermit thrush and ovenbird populations are lower in areas infested by worms. Possible reasons for the decline are that nests (on the ground) are more vulnerable to predation when located in the grasses promoted by worms, and a reduction in invertebrates fed to nestlings.

Expanding Risks

Several non-native earthworm species have been collected (so far) only from greenhouses or other places of indoor cultivation. But can we be sure that they are not being spread to yards, parks, and other places halfway to natural systems through movement of plants and mulch?

Earthworms are extremely difficult to manage once established.

Are these challenges the reasons why few official efforts to control earthworm spread have been adopted? Or is it the animals’ public image – they are widely regarded as “good” critters that enrich the soil and facilitate composting. Or is it that trying to control worms will require enhanced regulation of the nursery and green waste industries?

worms1 Amynthes photo; from Wisconsin DNR website

Wisconsin Is the Policy Pioneer

Wisconsin stands out for trying to address the issue! The state’s conservation and phytosanitary officials became alarmed when they detected Amynthas species in the University of Wisconsin Arboretum in 2013. This is the site of regular plant sales,a likely pathway for spread. Wisconsin now knows this genus of worms to be present in 21 counties, mainly along urban corridors. They have not yet been found in the state’s forests.

Wisconsin is acting to protect its forests despite Amynthas worms having been present in the United States for over a century: Snyder, Callaham and Hendrix 2010 say several species of Amynthas were documented in Illinois and Mississippi by the 1890’s. Some 15 species are recorded as established and widespread across the eastern United States (Reynolds and Wetzel 2004).

Wisconsin has classified the Amynthas genus as “restricted” – so their movement is now regulated. The risk of spread appears to be greatest through mulch produced from leaves collected in residential communities. The state held a workshop during which the regulated industry developed best management practices to address that risk. The Wisconsin Department of Natural Resources has posted a web page with information about identifying the worms and the BMPs. (Wisconsin DNR has also been a leader in tackling the firewood pathway.) The Wisconsin Department of Agriculture put the worm issue on the agenda of the National Plant Board in August 2016 and urged other states to take action.

The Wisconsin DNR webpage has

ID cards and other information to aid identification, g., photos of worms and the “coffee ground” soil they create;
a brochure with the state’s new “best management practices”
educate yourself and others to recognize jumping worms;
watch for jumping worms and signs of their presence;
ARRIVE CLEAN, LEAVE CLEAN – Clean soil and debris from vehicles, equipment and personal gear before moving to and from a work or recreational area;
only use, sell, plant, purchase or trade landscape and gardening materials and plants that appear to be free of jumping worms; and
only sell, purchase or trade compost that was heated to appropriate temperatures and duration following protocols that reduce pathogens.

What’s Up Where You Are?

What is your state doing to slow the spread of invasive earthworms?

Do nursery inspectors look for earthworms when approving plant shipments? Craven et al. 2016 findings re: higher impacts on plants as number of worm species rises demonstrate the importance of slowing spread of new species even into areas that already have some non-native earthworms.
Are professional associations of nurserymen and green waste recyclers educating their members about the damage caused by invasive earthworms and steps they can take to minimize worms’ spread to new areas?
Are organizations of anglers and gardeners in your state educating their members about the damage caused by invasive earthworms and steps they can take to minimize worms’ spread to new areas?
Are ecologists studying earthworm invasion impacts in other parts of the country? In non-forested ecosystems?
Are conservation organizations initiating or joining outreach efforts?
Can worm-education efforts be joined with h more robust public and private outreach focused on aquatic invaders, invasive plants, or firewood?

SOURCES

Bohlen, P.J., S. Scheu, C.M. Hale, M.A. McLean, S. Migge, P.M. Groffman, and D. Parkinson. 2004. Non-native invasive earthworms as agents of change in northern temperate forests. Front Ecol Environ 2004; 2(8): 427–435

Craft, J.J. 2009. Effects of an invasive earthworm on plethodontid salamanders in Great Smoky Mountans National Park. Thesis prepared at Western Carolina University.

Craven, D., M.P. Thakur, E.K. Cameron, L.E. Frelich, R.B. Ejour, R.B. Blair, B. Blossey, J. Burtis, A. Choi, A. Davalos, T.J. Fahey, N.A. Fisichelli, K. Gibson, I.T. Handa, K. Hopfensperger, S.R. Loss, V. Nuzzo, J.C. Maerz, T. Sackett, B.C. Scharenbroch, S.M. Smith, M. Vellend, L.G. Umek, and N. Eisenhauer. 2016.The unseen invaders: intro earthworms as drivers of change in plant communities in No Am forests (a meta-analysis). Global Change Biology (2016), doi: 10.1111/gcb.13446 available here.

Hendrix, P.F. 2010. Spatial variability of an invasive earthworm (Amynthas agrestis) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mountains National Park, USA. Biological Invasions DOI 10.1007/s10530-010-9826-4

Maertz, J.C., V. Nuzzo, B. Blossey. 2009. Declines in Woodland Salamander Abundance Associated with Non-Native Earthworm and Plant Invasions. Conservation Biology Volume 23, Issue 4 August 2009 Pages 975–981

Nuzzo, V.A., J.C. Maerz, B. Blossey. 2009. Earthworm Invasion as the Driving Force Behind Plant Invasion and Community Change in Northeastern North American Forests. Conservation Biology Volume 23, Number 4, 966-974.

Simberloff, D. and Von Holle, B. 1999. Positive interactions of nonindigenous species: invasional meltdown? Biological invasions 1, 21-32

Snyder, B.A., M.A. Callaham, C.N. Lowe, P.F. Hendrix. 2013. Earthworm invasion in North America: food resource competition affects native millipede survival and invasive earthworm reproduction. Soil Biology and Biochemistry 57, 212-216

Ziemba JL, Hickerson C-AM, Anthony CD. 2016. Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders. PLoS ONE 11(5): e0151591. doi:10.1371/journal.pone.0151591

When will invasive species get the respect they deserve from conservationists?

i`iwi in Hawai`i

photo from www.TheBirdBlogger.com; used with permission

Evidence is growing that invasive species are among THE major threats to conservation goals worldwide.

In 2015 the IUCN called invasive species the second most significant threat to those World Heritage sites around the world that have outstanding natural values. (Poaching is the greatest threat.) My October 21, 2015 blog showed that the IUCN report actually underestimated the impact of invasive species. I listed briefly the principal invaders in several U.S. National parks. Earlier blogs criticized the National Park Service for failing to regulate the movement of firewood (August 2015) and described the invasive threat to Hawai`i (earlier in October 2015).

Now a second study shows invasive species are a principal driver of species extinction. The authors assessed the prevalence of alien species as a driver of extinctions among plants, amphibians, reptiles, birds, and mammals (which are the best-studied taxa) post-1500 AD. Overall, 58% of extinct or extinct-in-the-wild species had been driven to extinction at least in part by invasive species. Invasive alien species are the second most common threat overall. Indeed, invasive species are the most common threat for vertebrate extinctions (62% of extinct or extinct-in-the-wild species faced threats from invasive species). Invasive species ranked fourth as a cause of extinction for plants: 27% of listed plant species were threatened by invasive species.

For those species with just a single driver of extinction, invasive species is the cause for 47% of mammals, 27% of birds, 25% of reptiles, and 17% of plants. In no case were invasive species identified as the sole threat to an amphibian species – although invasive species are their second highest threat.

Although the paper lists invasive species as second, their threat was virtually identical to that of “overexploitation”, the threat ranked first. That is, 124 out of 215 species studied were threatened at least in part by invasive species; 125 were threatened by overexploitation.

Other principal threats were overexploitation, agriculture, aquaculture, and – in the case of plants – residential and commercial development. Categories related to habitat loss ranked surprisingly low. Only 61 of the 215 cases listed agriculture and aquaculture as threats.

The authors reflect on whether invasive species are not themselves causal agents of extinction, but rather symptoms of the real causes, especially habitat destruction. They conclude that that is unlikely.

Instead, they suggest that invasive species impacts might often be underestimated, as many interactions – especially those between alien parasites and native hosts – are very hard to detect.

Not surprisingly, 86% of island endemic species had invasive species as one extinction driver. Nevertheless, continental organisms are also threatened — 14% of alien-related extinctions have been of species with mainland populations. These include eight amphibians, five birds, and six mammals. Most of these invader-threatened mainland organisms are from the Americas

Among the approximately 30 alien taxa named as extinction drivers are rats, cats, and trout as threats to other vertebrates such as birds and mammals. All three were also ranked highly as damaging invasives in the earlier IUCN report on World Heritage sites. Diseases – especially chytridiomycosis and avian malaria – were causal agents of extinction for amphibians and birds. Several herbivores – especially goats, sheep, and European rabbits – and alien plants were drivers of extinction for plant species.

Of course, outright extinction is not the only damage to biological diversity caused by invasive species. American chestnut, Fraser fir, and redbay are not extinct, but their ecological role has been virtually eliminated as the vast majority of these forest trees die off. Other tree taxa are on same road – ash and eastern hemlocks across wide expanses of their ranges; tanoaks; whitebark pines …

Invasive species pose major threats to biological diversity and other conservation goals. These damages are on top of the acknowledged threat of invasive species to agriculture, forestry, or economic groups. (See, for example, Lovett et al. 2016 discussed in my previous blog.) The role of invasive species in extinction described in this new paper suggest a long-standing bias among conservationists’ priorities. Too often, we have focused on species threatened by overexploitation – which is such easier to see and involves an obvious “villain”.

Nevertheless, a host of practical suggestions have been put forward to address the root causes of species introductions and spread. Often, these ask some or many of us to stop doing what we have been doing. But much meaningful conservation action requires someone to accept limits or to make sacrifices.

Will the conservation community – including grant-making foundations, federal and state agencies, and the many conservation non-governmental organizations ranging from the IUCN to local groups – now take up the challenge of implementing suggested actions and actively advocating for the funding needed for practical steps that will begin to bring this threat under control?

Sources

Bellard C, Cassey P, Blackburn TM. 2016 Alien species as a driver of recent extinctions. Biol. Lett. 12: 20150623. http://dx.doi.org/10.1098/rsbl.2015.0623 http://rsbl.royalsocietypublishing.org /

Lovett,G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig , F.T. Campbell , J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, S.L. LaDeau, and T. Weldy. 2016. Nonnative forest insects and pathogens in the United States: Impacts and policy options. Ecological Applications, 0(0), 2016, pp. 1–19. DOI 10.1890/15-1176.1

Available at www.caryinstitute.org/tree-smart-trade

Posted by Faith Campbell

Senate Hearing on Invasive Species Policy on Federal Lands

The Public Lands Subcommittee of the Senate Committee on Energy and Natural Resources held an oversight hearing on invasive species management on federal lands on April 28, 2016. This hearing is the result of lobbying effort by the Healthy Habitats Coalition, which drafted the initial bill and has worked for its passage for several years. One specific aim was to gather comments on S. 2240.

yellow start thistle photo by Peggy Greb, USDA ARS Bugwood # 1316001

The bill would, inter alia, require land-managing agencies to allocate their invasive species funds according to the following formula: 75% for on-the-ground activity; 15% for combined research and outreach; 10% or less for administrative costs. Priorities for federal agencies’ invasive species efforts would be set by state governors. The bill would also exempt some invasive species control programs from analysis under the National Environmental Policy Act (NEPA).

In December 2015 I posted a blog about an earlier hearing on the bill (H.R. 1485) held by the House Oversight Committee.

WHO WAS THERE?

Witnesses represented the USDA Forest Service, USDI Bureau of Land Management, the Wyoming Department of Agriculture, Healthy Habitats Coalition, and I, representing the Center for Invasive Species Prevention and Natural Areas Association. The witnesses’ written testimony and hearing video are archived here

Senators at the hearing were Chairman Barasso (WY), Franken (MN), and Hirono (HI). Senators Risch (ID), Hoeven (ND), and Gardner (CO) attended briefly. About 13 Congressional staffers were there, along with an audience of 15-20 and two from the press.

In their introductions, all senators spoke about the economic damage caused by invasive species Chairman Barasso said his bill – S. 2240 — is intended to fix western complaints about the ineffectiveness of federal agencies’ efforts. Senators Franken and Hirono agreed on the need for new tools and strategies and better coordination among actors. However, they expressed concern about some components of the bill.

At the end of the day …

The Healthy Habitats Coalition and the Wyoming Department of Agriculture support the bill. The USFS supported the bill’s goals and emphasis on collaboration but had some concerns. BLM praised changes made from earlier versions of the bill, hopes additional clarifications will be made, and explicitly opposed the categorical exclusion from NEPA. CISP and NAA (I) opposed the bill and suggested that the Senators take other actions to strengthen federal invasive species programs.

Will the bill move forward? I think action is unlikely … It is a shame that Congress has so little concern about invasive species. If there were a forward impetus, we could work with the Senators and Representatives to develop an approach that I think would be more productive.

Witness Statements

The administration witnesses took the usual approach, speaking about their agencies’ efforts and successes. Glenn Casamassa, USFS, noted the Service’s “leadership role” and spoke about programs across the agency. He estimated that the USFS treats ~400,000 acres per year for invasive species; the agency has restored about 2 million acres, with great success.

I question how these claims of success fit with the findings of USFS researcher Dean Pearson in Montana? I blogged about his studies in January. Pearson found that both invasion by alien forbs such as spotted knapweed and weed control efforts using either herbicides or grazing can lead to suppression of the native forbs. Furthermore, suppressing invasion by one set of plants – whatever the strategy used – often facilitates a secondary invasion by some other plant species that might cause greater changes to the system or that are harder to control. Such secondary invasions are likely any time a “strong” invaders relatively insensitive to the control method used is present. Often this secondary invader is cheatgrass.

Mike Pool, BLM, noted that invasive plants occupy ~79 million acres of lands it manages and described particular successes in CO and NM. Key is a comprehensive and coordinated response.

Doug Miyamoto, Wyoming Department of Agriculture, said S. 2240 would rely on local leadership; ensure consistent commitment by federal partners; specify a goal of reducing invasive species’ acreage by 5% annually; and halt delays caused by NEPA compliance. As an example, he cited a four-year delay in managing a USFS site following fire, which resulted in doubling of cheatgrass extent.

George Beck, a weed scientist at Colorado State University, representing the Healthy Habitats Coalition, took Federal agencies to task for inconsistent budgets; lack of cooperation; lack of coordination with states; and using NEPA as an excuse for delays. Not expecting leadership from the federal government, he called on Congress to enact binding requirements through S. 2240.

Faith Campbell, representing CISP and the Natural Areas Association. I agreed that Federal leadership has fallen short and that the Nation needs a comprehensive invasive species program. I raised concerns about provisions of S. 2240:

Funding allocations would undercut essential research, outreach, and other activities aimed at development and implementation of effective tools;
These restrictions are exacerbated when combined with the unrealistic goal of bringing about 5% per year net reduction in invasive species populations;
New reporting and coordination requirements that might further delay needed actions;
Priorities in managing invasive species on national lands should reflect the national perspective, not be set by states’ governors.
The NEPA Categorical Exclusion could expose the environment to additional damage.

I called on the Senators to take several practical steps:

Amend the Lacey Act to enable the Fish and Wildlife Service to

apply scientific risk assessment tools in evaluating species proposed for importation;
act quickly when confronted by an emergency.

Plus clarify FWS’ authority to regulate

all animal taxa (in coordination with USDA);
the threat to wildlife from disease; and
interstate movement of species already listed under the Lacey Act as “injurious”.

Provide higher appropriations for key agencies: APHIS, FWS, EPA, Corps of Engineers, and the land and water-managing agencies.
Conduct oversight hearings at which Senators ask Secretaries (of USDA & USDI) and their Assistant/Under secretaries about their efforts to address invasive species, specifically:
- Has the USFS implemented its 2011 internal directive amending the Forest Service Manual? (The directive calls for integrating invasive species activities across programs on National forests and grasslands.)
- Why has neither the USFS nor NPS adopted a nation-wide policy to limit campground visitors from bringing their own firewood?
- Has/when will the Council on Environmental Quality collaborate with the National Invasive Species Council re to develop guidance on applying the National Environmental Policy Act (NEPA) to invasive species management?
Ensure that when the Senate confirms nomimees to be new secretaries or assistant/under secretaries of USDI and USDA in 2017, those nominees are asked about their goals with regard to invasive species prevention and management.

Questions from the Senators

Much of the discussion centered around the bill’s language excluding invasive species control programs from NEPA. Chairman Barrasso, Miyamoto of Wyoming, and Beck all said NEPA compliance had caused damaging delays and described the Categorical Exclusion language in the bill as “limited”.

Pool said BLM has successfully used programmatic environmental impact statements to evaluate options over large areas ahead of time in order to act quickly in a crisis. Pool said that BLM distinguishes between catastrophic wildfire – when no NEPA analysis is required; When deciding how to respond to long-lived problems that affect hundreds of thousands of acres, BLM wants to inform and engage the public – and NEPA is a good process to do that.

Casamassa said USFS emergency responses on significant burned areas are not subject to NEPA; instead its actions are guided by Forest Plans. He supported rulemaking to clarify the bill’s categorical exclusions for invasive species.

I opposed a NEPA Categorical Exclusion because all actions – even those based on good intentions – have downsides that need to be evaluated. (See discussion of Pearson’s research from my blog in December.) APHIS has used programmatic EIS to help agency move quickly. I expressed frustration that CEQ has stonewalled NISC on developing guidance.

(Whether the NEPA exemption is “limited” is open to discussion! It would apply to projects on federal lands that are or will be “located in a prioritized, high-risk area” and treat invasive species within 1,000 feet of, inter alia, a water body or waterway; a railroad line or roadside; a water project; a utility or telephone infrastructure or right-of-way; a campground; a National Heritage Area or National Monument; a park or other recreational site; a school; or “any other similar, valuable infrastructure”.)

In response to Chariman Barasso’s question about the Early Detection/Rapid Response plan recently released by the National Invasive Species Council, Beck said that in his view states should take the lead in slowing the spread of species within the country. He criticized federal agencies’ failure to halt new introductions.

Senator Franken expressed dismay that only one of the five witnesses’ written statements mentioned climate change as a factor re: invasive species. In response, the USFS and BLM stressed their efforts to adapt.

Senator Hirono asked whether the prescribed funding allocations in S. 2240 (75% for “on the ground” work; 15% for research and outreach combined; 10% for administration, including strategy and oversight) would hamper needed actions? She cited the need for research to develop tools to manage the sudden `ohi`a death fungus [described as “ohia wilt” here.] Casamassa of the USFS said the agency’s spending on invasive species is already close to the S. 2240 funding allocation. Nevertheless, the agency would sometimes need greater flexibility. On the other hand, Beck said research on invasive species should be left to other agencies, such as the U.S. Geological Survey and Agriculture Research Service.

Senator Hirono expressed concern that the bill’s requirement that agencies use the “least costly” method would expand use of pesticides – an approach that concerns Hawaiians.

Senator Hirono asked Campbell whether the 5% reduction goal is do-able? Especially re: insects and pathogens? I replied that all agencies are dealing with hundreds of invasive species at a time. Many of the insects and pathogens – as well as the aquatics – can’t even be detected, much less the extent of invasion. Managers lack tools to reduce their extent. I also worried that the 5% goal will put pressure on agencies to tackle easily measured invasive species e.g., plants, and ignore others.

Chairman Barrasso concluded the hearing by telling me that he thinks our views are not mutually exclusive. He sees the need for both prevention and control of widespread species.

Posted by Faith Campbell & Phyllis Windle

Feral Hogs: numbers climbing, threats to soils & ecosystems increasing, no control in sight

Introduced wild hogs (Sus scrofa) threaten ecosystems across the continent and on islands ranging from Hawai`i to the Caribbean.

large_hog_damage (MO) feral hogs in Missouri

Pigs are the ultimate survivors – highly adaptable and prolific. Most of the damage is done by their rooting for plant parts and invertebrates in the soil, and by wallowing to cool themselves and fend of biting insects. Depending on soil type (density, moisture level, compaction), pigs may root to depths of three feet below the surface (USDA APHIS EIS).

Feral hogs consume primarily plant matter. They prefer hard mast – e.g., acorns, beechnuts, chestnuts, or hickory nuts. Pigs can be formidable competitors with native wildlife for this nutritious food. Feral hogs also eat algae, fungi, invertebrates such as insects, worms, crustaceans, and bird and reptile eggs. In addition, they feed on small animals, including reptiles, fish, amphibians, ground-nesting birds, and young of wild game and domestic livestock. They even feed on larger animals – although it is not clear whether they kill such animals or only scavenge their carcasses (USDA APHIS EIS).

Since pigs lack sweat glands, they wallow in water and mud to cool off. Some wallow sites are used for years. Adjacent areas are usually denuded of vegetation and the soils are compacted. Wallows are commonly located in or adjacent to riparian or bottomland habitats (USDA APHIS EIS).

Despite the apparent damage, only a few studies address the feral hogs’ impacts on soil structure, chemistry, bulk density and nutrient cycling. The conclusions of those studies are mixed (USDA APHIS EIS).

In Great Smoky Mountains National Park, feral pigs are reported to “plow up” areas in search of bulbs, tubers and wildflowers and to consume small mammals, snakes, mushrooms, bird eggs, and salamanders. (The Smokies are a center of endemism for salamanders.) Wallows are said to contribute significantly to stream sedimentation, thereby harming aquatic life.
Furthermore, feral hogs contribute to both human and animal disease. Their feces contaminate water and soil with coliform bacteria and Giardia which are both a threat to human health. Some of the wild pigs also carry Pseudorabies, a disease that is almost always fatal to mammals, including such important wildlife species as black bear, bobcat, elk, white tailed deer, red fox, grey fox, coyote, mink, and raccoon. Pseudorabies from wild boar can survive in humid air or water for up to seven hours and in plants, soil, and feces for up to 2 days.

Unfortunately, the United States’ population of introduced wild pigs has dramatically increased since 1990. People are to blame.

States with feral hog populations; provided by John Mayer, US Department of Energy, Savannah River National Laboratory

According to John J. Mayer, the number of states with established wild boar populations has risen from 19 in the 1990s to 37. The total number of feral hogs has risen from an estimated 1 to 2 million animals to a range of 4.4 to 11.3 million (Mayer).

The overwhelming majority of the feral hogs is found in only 10 states –AL, AR, CA, FL, GA, LA, MS, OK, SC, TX. Texas has the largest numbers, 30 to 41% of the U.S. total, depending on whether one is counting the states’ animals by mean, maximum, or minimum estimates.

Why have people transported feral pigs to so many new places over the last 20 years? Largely because hunters wanted an exciting game animal to pursue (USDA APHIS EIS; Mayer). In Tennessee, populations of feral swine (probably released by farmers to forage for themselves) were relatively stable and confined to only a few counties from the 1950s through the 1980s. However, since a statewide, year-round, no bag-limits hunting program was instituted in 1999, pig populations have expanded rapidly. In 2011, nearly 70% of counties had pockets of feral swine (USDA APHIS EIS).

But hunting is not an effective means of controlling the animals’ populations and damage. Mayer reports that sport hunters remove about 23% of a wild pig population annually. Models demonstrate that 50 – 75% of a wild pig population must be removed annually, year after year, in order to reduce or eradicate that population (J.J. Mayer pers. comm]

Mayer says there are currently no effective management tools or options to reduce or control feral hog populations in most situations. I note that the Hawaii Volcanoes and Haleakala National parks have been able to eradicate feral pigs through determined efforts.

Missouri is one state that is tackling feral hogs aggressively. In January, the Missouri Conservation Commission approved changes to the Wildlife Code of Missouri that would prohibit the hunting of feral hogs on lands owned, leased, or managed by the Missouri Department of Conservation. A public comment period on the proposed regulation change will run from April 2 through May 1. After considering the citizen input and staff recommendations, the Commission will reach a decision whether to finalize the new regulation – probably in September. (Missouri has quite extensive material on feral hogs posted here
Meanwhile, the Missouri Department of Conservation has reached out to several partners to strengthen its increase the number of feral hog traps it can place and enhance communication to the public. These partners include such agricultural organizations as the Missouri Farm Bureau and Missouri Pork Producers; and such conservation organizations as the National Wild Turkey Federation and two quail associations.

New York has gone farther; it has adopted a policy of eradicating Eurasian wild boar from the state. To achieve this goal, the state in October 2013prohibited importing, breeding, or releasing Eurasian boars. As of September 2015, it has been illegal to possess, sell, distribute, trade or transport Eurasian boars in New York. Hunting or trapping of Eurasian boars is illegal except for law enforcement officers, farmers, and landowners authorized by the Department of Environmental Conservation (DEC). The hunting ban was adopted in order to minimize breakup of sounders so as to facilitate eradication trapping by trained conservation officers. For more information, visit the DEC website.

Sources
Mayer, J.J. 2014. Estimation of the Number of Wild Pigs Found in the Unted States. August 2014 SRNL-STI-2014-00292, Revision 0.

U.S. Department of Agriculture Animal and Plant Health Inspection Service
Final Environmental Impact Statement. Feral Swine Damage Management: a National Approach May 27, 2015

Click to access 2015%20Final%20EIS%20Feral%20Swine%20Damage%20Management%20-%20A%20National%20Approach.pdf

Posted by Faith Campbell

Fed up by lack of action on invasive species? Let’s pressure the right targets!

On December 1, the House Oversight Committee, Subcommittee on Interior, held a hearing on invasive species. This hearing was apparently held at the request of the ranking Democrat, Brenda Lawrence of Michigan. Ms Lawrence is most concerned about aquatic invaders in the Great Lakes. Chairwoman Cynthia Lummis is from Wyoming, so her focus is on invasive plants on western rangelands.
Chair Lummis opened the hearing, but left promptly. Other subcommittee members who were present for varying lengths of time were Paul Gosar (R-AZ), Ken Buck (R-CO), Gary Palmer (R-AL), Brenda Lawrence (D-MI), and Stacey Plasket (D-USVI) ; from full committee: Will Hurd (R-TX).

The witnesses were the newly appointed executive director of the National Invasive Species Council (NISC), Jamie Reaser; the president of the Reduce Risk from Invasive Species Coalition (RRISC), Scott Cameron; Dr. George Beck of Colorado State University, representing the Healthy Habitats Coalition (HHC); and Dr. Alan Steinman, expert on aquatic invaders from Grand Valley State University in Michigan.
This hearing followed those in past years that had been stimulated by the HHC. Both HHC and Congressional members expressed great frustration that the federal government is not putting sufficient effort into stopping or reversing the spread of invasive plants on western rangelands.
The December hearing – like its predecessors – focused the criticism on NISC. I think this focus is misguided. NISC has no independent authority or power; it was created to coordinate agencies’ actions, not to substitute for them. Its staff lack sufficient rank to tell agencies what to do.
In § 4 of Executive Order 13112, NISC’s duties are listed as providing national leadership through (a) overseeing implementation of this order, seeing that Federal agencies’ activities are coordinated, complementary, cost-efficient, and effective, …; (b) encouraging planning and action at local, tribal, State, regional, and ecosystem-based levels …; (c) developing recommendations for international cooperation …; (d) developing, in consultation with the Council on Environmental Quality, guidance to Federal agencies pursuant to the National Environmental Policy Act (NEPA)…; (e) facilitating development of a coordinated network among Federal agencies to document, evaluate, and monitor IAS impacts …; (f) facilitating establishment of an … information-sharing system …; and (g) preparing a national Invasive Species Management Plan every two years.
NISC has fallen far short of these requirements. It has not succeeded in developing guidance on NEPA – at least in part because CEQ has not cooperated. Most glaringly, NISC has issued only two Management Plans over 15 years — the most recent in 2009. All Members at the hearing complained to Reaser about this failure. Members see the Plan as key to setting priorities and ensuring that funds are well-spent.

All Members seemed to think that NISC actually should carry out on-the-ground activities and direct agencies’ priorities. Some want NISC to overcome federal agencies’ alleged foot-dragging in helping local groups eager to attack local problems, or to pressure Native American tribes to cooperate.

While I share the critics’ frustration about federal agencies’ inaction, I believe the productive approach is to apply pressure on – and where deserved, support for – those who have the authority and power to act, but who often choose not to. These are:
• heads of agencies and departments, especially the secretaries of Agriculture and Interior and their Under and Assistant secretaries;
• the President;
• budget staffs of these and other relevant agencies;
• the Office of Management and Budget;
• Members of the Congressional appropriations committees.

If these people think that dealing with invasive species is politically important, they will do so. If they don’t hear from their constituents about invasive species, they will focus on other issues.

At the hearing, Scott Cameron, of RRISC, said that what is missing is commitment at the Assistant/Under Secretary Level. Such a commitment would both drive coordination among agencies at headquarters and provide “cover” for regional staff trying to work together. He feels that a new Management Plan is useful but not sufficient. Scott made several recommendations intended to raise the political visibility of invasive species issues:
1) NISC submit annual work plan to Congress – he thought this would get political level attention in the departments;
2) NISC serve as forum to coordinate with regional governors’ associations;
3) NISC create national network of regional early detection/rapid response efforts;
4) NISC serve as forum for regional officials of land-managing agencies to coordinate and work together – this might succeed in getting attention of agency leadership and OMB;
5) NISC ensure coordination of priorities and approaches by member agencies at headquarters level; and
6) NISC evaluate best practices by other governments, propose their adoption by the United States.

Dr. Beck, of HHC, reiterated his constituency’s complaint that there has been little progress on invasive species problems despite three decades of effort. He blamed the lack of leadership by NISC – without saying how staff can “lead” the political appointees who head agencies! He called – again – for abolition of NISC and transfer of its $1 million budget to “on the ground” programs. Beck also decried inconsistencies in agencies’ budgets, lack of collaboration with states and local groups in setting priorities, and NEPA having become an excuse to avoid taking action.

HHC has promoted introduction of bills in both the House and Senate – H.R 1485 & S. 2240 – which would require:
• strategic planning;
• cooperation with states;
• categorical exclusion from NEPA review for efforts to protect high-priority sites;
• 5% annual reduction in weed species’ extent; and
• allocation of agencies’ invasive species funds according to the following formula: 75% for on-the-ground activity; 15% for combined research and outreach; 10% or less for administrative costs.

Of these recommendations, I think the proposed dropping of environment reviews of invasive species management programs – especially in “high priority” sites of high ecosystem values – would be a disaster. Management programs have environmental impacts, too; and some approaches cause more harm than good. For example, use of herbicides to eliminate knapweeds has sometimes resulted in takeover of the site by non-native annual grasses that are even more difficult to control.

Also, I think the proposed funding allocation is very unwise. Research and outreach often contribute enormously to control or containment of invasive species. I have been unable to get straight answers from the USDA Forest Service about how such an allocation would affect their programs – which are divided among three separate entities – Research, State and Private Forestry, and National Forest System.

HHC is very active in promoting its position – and those of us who think differently are not yet being heard in Congress.

I think there is room to work with members of the House Oversight Committee to focus more attention on the agencies’ political leadership – where it belongs and where pressure might have an effect. Rep. Lawrence seems interested in continuing efforts. Rep. Hurd of Texas asked about steps to prevent plant pest introductions (none of the witnesses knew about APHIS programs). Furthermore, a second Michigander, Rep. Dan Benisheck, and a Californian, Rep. Mike Thompson, co-chair the Invasive Species Caucus. Although none of them has yet expressed concern about tree-killing pests, given where they are from they might be persuaded to engage.

At present, the only Congressional champion for effective invasive species programs – especially as regards tree-killing pests – is Senator Leahy of Vermont. He has helped prevent further cuts in budgets for APHIS and USFS. We need more friends in Congress.

I urge you – and your friends! – to contact your Representatives and Senators to explain how invasive species are damaging important ecological and economic resources in your state. Ask them to work with their colleagues to support and improve federal programs aimed at preventing new introductions, containing species already introduced, and developing effective methods to reduce pests’ impacts and restore native forests.

Posted by Faith Campbell

New IUCN report notes invasive species threat to World Heritage Sites – Including U.S. National Parks

The World Conservation Union (IUCN) has just released a report, IUCN World Heritage Outlook 2014 (for press release, click here; for the full report, click here)
that names invasive species as the second most significant threat World Heritage sites with outstanding natural values. (Poaching is the greatest threat).

World Heritage sites have “outstanding universal values” – either natural or cultural. Natural sites are areas either of exceptional beauty or representative of major stages of Earth’s history, significant ongoing ecological processes, or significant habitats for biodiversity and threatened species.

The 2014 assessment examined 229 natural World Heritage sites and found that 104 are affected by invasive species. Unsurprisingly, island sites are especially heavily impacted. Two-thirds of the affected island sites (24 out of 36) are in the tropics.

The most widespread or common invaders are plants; they are named in 55 of the 104 affected sites. Invasive vertebrate animals affect at least 12 sites. These frequently include fish (mostly trout), cats, and rodents (especially rats).

The report calls for effective management strategies to protect the World Heritage sites. Such strategies include well-defined plans as well as strict bio-security measures, including limiting materials entering the site or the eradication of problem-causing species. Ideally, these actions involve local communities. Among the 104 natural World Heritage areas affected by invasive species, 87 have management projects addressing at least some invasive species or related issues.

According to the report, future invasive species management will be even more challenging, especially because of climate change. Climate change, itself, could become the biggest threat to natural sites in future.

dead sweetbay in Big Cypress National Preserve, Florida

The United States has 21 World Heritage sites. Nine were chosen for their outstanding natural values. These include the following National parks: Everglades, Grand Canyon, Great Smoky Mountains, Hawaii Volcanoes, Redwood, Yellowstone, and Yosemite National parks; and – jointly with Canada – Kluane / Wrangell-St. Elias / Glacier Bay / Tatshenshini-Alsek and Waterton-Glacier National parks.

Several of these natural wonders are well known to be threatened by invasive species – including some tree-killing insects and pathogens.

Everglades National Park. In Everglades, pythons have decimated populations of small to medium native mammals. Lionfish are killing vast numbers of fish in the shallow bay. Numerous invasive plants, especially Australian pine, Melaleuca, Brazilian pepper, and old world climbing ferns transform the natural sawgrass prairie and mangroves. Some, e.g., Melaleuca, are under control thanks to persistent effort over decades.

Laurel wilt has almost eliminated swamp bay trees from the hammocks. Bromeliad weevil has killed many bromeliads in 12 genera (of the 16 present in Florida).

Tillandsia utriculata bromeliad in Florida

Great Smoky Mountains National Park. The outstanding biological diversity of the forested Great Smoky Mountains National Park has been severely undermined by chestnut blight, hemlock woolly adelgid, balsam woolly adelgid; and is now under attack by more recent invaders, including beech bark disease, emerald ash borer, and thousand cankers disease of walnut. Descriptions of all these pests are available here. At ground level, feral hogs damage plants, soil-dwelling invertebrates and small vertebrates, even birds. Rainbow trout compete with native trout in the streams. More than 380 non-native plants compete with the native species. The Park’s website features another invader, the Asian jumping worm (Amynthas agrestis), which has been introduced through bait.

The Great Smoky Mountains are the center of biological diversity for salamanders which are likely soon to face danger from the “Bsal” pathogen – unless the Fish and Wildlife Service acts to restrict imports of salamanders by the pet trade. See how CISP tries to counter this threat.

Hawaii Volcanoes National Park. As I wrote in my blog of October 7, Hawaii Volcanoes National Park is fighting feral hogs, goats, and a plethora of invasive plants (the Park’s flora contains nearly twice as many exotic flowering plants as native species). The Park’s birds are threatened by two non-native diseases, avian pox and avian malaria. As noted in the earlier blog, Hawaii Volcanoes has also been invaded by koa wilt and `ohi`a rust; and is about to be invaded by `ohi`a wilt.

Web-based information from several parks in the western part of the continent focuses on the threat from invasive plants: Grand Canyon, Olympic, Yellowstone, and Yosemite. Redwoods National Park notes the damage caused by sudden oak death to its principal hardwood species, tanoak. Yellowstone National Park has a website describing its whitebark pine forests and mentioning that up to 30% of the taller whitebark pines have been attacked by white pine blister rust; I could find little information about the disease’s impact on the Park’s limber pines, which are also susceptible.

Yosemite National Park has a website with a table listing 16 non-native insects and pathogens that could threaten trees in the park. White pine blister rust is already present in the Park’s sugar pines. I am pleased to see that the website features goldspotted oak borer and the risk of pest introduction via firewood. I just wish Yosemite actually prohibited visitors from bringing firewood into the Park! And carefully restricted commercial suppliers! I addressed Yosemite’s failure to protect itself in my blog of 10 August.

The National Parks Conservation Association is the principal NGO that advocates for protection of the National parks. It issued a report in 2008 that found invasive species were a limited concern in 90% of the parks evaluated, a widespread or chronic concern in 38%. In Hawaii Volcanoes specifically, the natural resources were ranked in “poor” condition due primarily to non-native plants and animals.

Many individual parks have “Friends” groups ….

I ask these groups to help the National parks counter invasive species. To be effective, they need to go beyond the many volunteer “weed pulls” and outreach programs educating park visitors who might transport invasive species (for example, boaters and fishermen who can spread New Zealand mudsnails, rock snot, and invasive mussels; and campers who carry firewood that can transport pests). I ask them to also lobby for policies that would prevent invasions and for increase funding for the parks’ resource management programs (the programs that tackle invasive species). I suggest specifically that supporters of National parks advocate for improvements in programs run by the USDA’s Animal and Plant Health Inspection Service or the U.S. Fish and Wildlife Service. These agencies, more than any other, determine whether prevention succeeds or fails.

Posted by Faith Campbell

Hawaii’s unique forests now threatened by insects and pathogens – APHIS & State should act

We have known since Darwin that oceanic islands can be cradles of speciation & endemism. Hawai`i exemplifies the phenomenon. Ninety-eight percent of native flowering plants are endemic (Cox). The density of native insect species in Hawai`i is higher than on mainland North America (Yamanaka).

We have known since Elton or earlier that oceanic islands are highly vulnerable to bioinvasion because their unique species did not evolve defenses against predation, herbivory, competition, or diseases; or the ability to adapt to changed soil chemistry or increased fire frequency.

Chapter 8 of the Office of Technology Assessment study of harmful invasive species states:

“Hawaii has a unique indigenous biota, the result of its remote location, topography, and climate. Many of its species, however, are already lost, and at least one-half of the wild species in Hawaii today are non-indigenous. New species have played a significant role in the extinction of indigenous species in the past and continue to do so. Hawaii, the Nation, and the world would lose something valuable as the indigenous fauna and flora decline.”

I apologize for not addressing the disasters wreaked on Hawai’i’s fauna and non-arboreal flora by invasive mammals and birds, plants, and such animal diseases as avian malaria and avian pox. For more on these topics, see the other sources listed below and the websites maintained by the Hawai`i Invasive Species Council and Coordinating Group on Alien Pest Species. Cox notes that alien species span all trophic groups and threaten the complete replacement of the native terrestrial biota.

Outside of land clearing for ranches and other uses, much of the damage to Hawaii’s native forest trees has been caused by introduced mammals – especially pigs and goats; and invasive plants. Few of the enormous number of non-native insects that have established in Hawai`i appear to have attacked native trees. More than 2,600 non-native insects have been introduced; their number equals three-quarters of the NIS insects established in North America, yet Hawai`i constitutes less than 0.01% of the area of North America. The ratio of non-native to native insect species is higher for Hawai`i than for the other geographic areas studied by Yamanaka and colleagues (mainland North America, “mainland” Japan, and two offshore Japanese islands) (Yamanaka).

More than 13% of the non-native insects (=~350) in Hawai`i were introduced intentionally for biological control of agricultural pests and non-native plants (Yamanaka). Cox, Elton, and the Office of Technology Assessment discuss briefly the sometimes damaging effects of these deliberate introductions.

I am aware of only one NIS insect that has seriously threatened a native tree species: the Erythrina gall wasp, which killed many native wiliwili trees as well as lots of introduced coral trees planted in towns and as windbreaks. Biocontrol agents have helped prevent continuing damage from the gall wasp.

Disease pathogens have so far proved greater threats to Hawaiian native trees than introduced insects. Koa wilt is killing koa, especially at lower elevations. It is not certain whether the pathogenic Fusarium fungus is introduced or native; it has been found on all four major islands. Koa is second only to `ohi`a (see below) in abundance in mid to upper elevation Hawaiian forests. It is extremely important ecologically and culturally (koa was the tree from which large, ocean-going canoes were made). Koa also has a wood valued for a range of uses.

`Ohi`a lehua is the most widespread tree on the Islands, dominating approximately 80% of Hawai`i’s remaining native forest (about 965,000 acres, 1500 square miles). These forests are home to Hawai`i’s one native mammal (Hawaiian hoary bat) and 30 species of forest birds (Loope and LaRosa). One threat to `ohi`a comes from `ohi`a or eucalyptus rust. Detected in April 2005, it had spread to all the major islands by August. Fortunately, the strain of `ohi`a rust established in Hawai`i is not very virulent on `ohi`a, but it has killed many plants of an endangered native shrub, Eugenia koolauensis and in Australia it has killed many plants in the Myrtaceae family. Hawaiian conservationists worry that a different, more virulent, strain might be introduced on plants or cut foliage shipped to the Islands from either foreign sources or the U.S. mainland.

A new, apparently more damaging, pathogen was detected in 2010. This new disease is caused by two newly discovered species of the fungal genus Ceratocystis — Ceratocystis lukuohia and C. huliohia. By October 2015 the disease has killed 50% of the `ohi`a trees in several scattered locations totaling 6,000 acres on the southeast lowlands of Hawai`i (the “Big Island”). Tree mortality was nearing the boundary of Hawaii Volcanoes National Park. Hawaii Volcanoes pioneered methods for controlling invasive pigs and plants that threatened to destroy the Park’s forests. Through 40 years of sustained effort, Hawaii Volcanoes has brought those threats under control. Now the Park faces loss of its invaluable `ohi`a forest to this pathogen – which will be infinitely harder to keep out of the Park. (For updates on “rapid ohia death” visit the write-up here.)

The Hawai`i Department of Agriculture has adopted an emergency regulation aimed at preventing transport of infected wood or tree parts from the Big Island to other islands.

Although tree-killing insects and pathogens have so far not been as damaging in Hawai`i as might be expected, the Islands are highly vulnerable due to the large volumes of cargo and people from around the globe which land on the Islands and the few tree species native there. The Erythrina gall wasp has island-hopped from the east coast of Africa to Hawai`i and many islands in between. `Ohi`a rust is native to tropical America and probably reached the islands on cut stems used in floral decorations. It is unknown where the Ceratocytis fimbriata strain evolved or how it reached Hawai`i.

USDA APHIS is responsible for preventing introduction of new plant pests to Hawai`i from non-U.S. jurisdictions (as well as from Guam). APHIS has traditionally paid little attention to plant pests that are thought likely to threaten “only” Hawai`i but not plant (agricultural) resources on the mainland.

Hawaiian authorities are responsible for preventing introductions from the Mainland – but they struggle with inadequate resources to address the huge volumes of incoming freight and they sometimes hesitate to act. (Hawai`i Department of Agriculture considered restricting shipments of foliage in the Myrtacea to minimize the risk of introduction of a new strain of `ohi`a rust, but in the end did not adopt such a measure.)

Hawai`i’s unique biota is an irreplaceable treasure. All Americans should act to prevent introduction additional introductions to the Islands.

SOURCES:
Cox, George W. Alien Species in North America and Hawaii Impacts on Natural Ecosystems 1999
Elton, Charles S. The Ecology of Invasions by Animals and Plants 1958; see especially Chapter 4: The Fate of Remote Islands
Loope, L. and LaRosa, A.M. `Ohi`a Rust (Eucalyptus Rust) (Puccinia psidii Winter) Risk Assessment for Hawai`i
U.S. Congress Office of Technology Assessment. 1993. Harmful Non-Indigenous Species In the United States. OTA-F-565; available at http://govinfo.library.unt.edu/ota/Ota_1/DATA/1993/9325.PDF

Yamanaka, T., N. Morimoto, G.M. Nishida, K. Kiritani, S. Moriya, A.M. Liebhold. 2015. Comparison of insect invasions in North America, Japan and their Islands. Biol Invasions DOI 10.1007/s10530-015-0935-y

Posted by Faith Campbell